Landfill fuel gas production.

burying a huge amount of trash and loose organics like potato's then putting a natural gas extractor on top will slowly convert it into contaminated dirt and fuel gas. You can then use the fuel gas and clean the contaminated dirt in some way later.
Real landfills have flare towers from how much methane they make. It would be cool to show off in game. It's a fuel source that is being wasted in the real world right now and it would be cool to show a practical use for it in game.

Something that can be added to this to help expand on how the landfill works with waste and organic waste is this video that came out recently, talking about the engineering of real landfills. https://youtu.be/HRx_dZawN44
Something that can be utilized is open mines or quarries to help keep the soil polution low, and when the landfill is full if its covered with a layer of soil this could potentially be a system on its own to allow a natural production of fuel gas with a building slowly destroying the waste under the soil in an area and converting it to fuel gas. Similar in idea to how a forestry works, only you're dealing with a proper waste management building to dump waste into a designated area and allow fuel gas conversion if the conditions are properly met. This can also be an interesting addition to the terraforming system of the game where the waste cells that are buried are deleted by the waste treatment plant and letting the ground settle over time as the waste is converted.